Image display

ABSTRACT

An image display device has a plurality of electrodes that control a beam between a group of linear cathodes ( 2 ) and a screen ( 8 ) with a phosphor layer, and is provided with a circuit ( 31 ) for generating a beam track offset signal, which generates a signal for slightly oscillating one of the beams horizontally, a PIN photodiode ( 33 ) for detecting the emission amount of the phosphor layer for this beam, a comparator ( 35 ) for generating a beam irradiation position misalignment signal based on the detected emission amount, an integrating circuit ( 36 ) for generating a beam position control signal in correspondence with the beam irradiation position misalignment signal; and a horizontal deflection electrode driving circuit ( 39 ) for driving a horizontal deflection electrode ( 6 ) in accordance with the beam position control signal. With this configuration, misalignments of the position of the beam spot and the phosphor stripes on the screen, which are caused for various reasons, can be suppressed, and an image display device is obtained, in which a deterioration of the image quality, such as color misalignments, does not occur.

TECHNICAL FIELD

The present invention relates to an image display device used in colortelevision receivers and terminal displays for computers, etc.

BACKGROUND ART

FIG. 6 is a schematic exploded perspective view of a conventional imagedisplay device. In this conventional image display device, a rearelectrode 1, a group of linear cathodes 2 serving as a beam source, abeam extraction electrode 3, a control electrode 4, a focusing electrode5, a horizontal deflection electrode 6, a vertical deflection electrode7, and a screen 8 are arranged in this order from the rear towards theanode, and are stored inside a vacuum container (not shown in thedrawings).

The group of linear cathodes 2 serving as a beam source is made byextending a plurality of linear cathodes horizontally, so as to generateelectron beams that are distributed linearly in a horizontal direction.A plurality of these cathodes is arranged at predetermined intervals ina vertical direction. In this conventional image display device, theintervals between the linear cathodes in the vertical direction are 5.5mm, with a number of 19 cathodes denoted 2 a to 2 s. However, in orderto avoid making FIG. 6 too complicated, only four linear cathodes from 2a to 2 d are shown. The linear cathode 2 a to 2 s are made by applyingan oxide cathode material to the surface of a tungsten wire with adiameter of 10-30 μm, for example. These linear cathodes are thenoperated for a constant time in sequence from the upper linear cathode 2a to the lower linear cathode 2 s, so that each cathode emits anelectron beam every 18 horizontal scanning periods.

In addition to prevent the generation of electron beams from linearcathodes other than predetermined linear cathodes, the rear electrode 1also has the function to ensure that electron beams are emitted only inthe direction of the anode. The vacuum container is not shown in FIG. 6,but depending on the circumstances, the rear electrode 1 can be takenand formed in one piece with the vacuum container.

The beam extraction electrode 3 is made of a conductive board 11provided with a plurality of through holes 10 and has the function todivide and select a plurality of electron beams emitted from the group 2of linear cathodes horizontally via the through holes 10. On the beamextraction electrode 3, the through holes 10 are arranged on theconductive board 11 with constant horizontal pitch, in opposition to thelinear cathodes 2 a to 2 s. In this conventional image display device,the horizontal pitch of the through holes 10 is 1.28 mm and there are107 through holes 10 in the horizontal direction.

The control electrode 4 is made of 107 long vertical conductive boards15, which have through holes 14 that are positioned in opposition to thethrough holes 10 of the beam extraction electrode 3. However, in orderto avoid making FIG. 6 too complicated, only nine conductive boards 15are shown. Furthermore, based on the image signal for each section, thecontrol electrode 4 simultaneously modulates the throughput of theelectron beams that are divided into 107 horizontal sections.

Each section is divided into two pixels, and as each pixel has threeprimary colors (phosphors) of R (red), G (green), and B (blue), the sixsignals of 2 (pixels)×3 (primary colors) that correspond to each sectionare synchronized with the horizontal deflection, described later, andare then added one after another in time division (within one horizontalscanning period).

The focusing electrode 5 is made of a conductive board 17 that has aplurality of through holes 16, which have the function to focus theelectron beam. The through holes 16 in this conductive board 17 areformed in positions opposing the through holes 14 formed in the controlelectrode 4.

The horizontal deflection electrode 6 is made of a pair of a comb-shapedconductive boards 18 and 18′ arranged vertically along both horizontalsides of the through holes 16 formed in the focusing electrode 5, andits function is to simultaneously deflect the electron beam that isdivided into 107 sections in a horizontal direction, so that the twogroups of the primary color phosphor stripes R, G, and B on the screen8, which will be described later, are irradiated successively in sixstages and emit light.

The vertical deflection electrode 7 is made of a pair of comb-shapedconductive boards 19 and 19′ arranged horizontally, in the space betweenvertically neighboring through holes 16 formed on the focusing electrode5. With these two conductive boards 19 and 19′, the voltage for verticaldeflection is applied, and the vertical deflection electrode 7 deflectsthe electron beam vertically. Here, the vertical deflection electrode 7deflects the electron beam which is emitted by the 19 linear cathodes 2a to 2 s in 12 stages each, or in other words, 12 horizontal scanningline segments each, and 228 horizontal scanning lines are drawn in avertical direction on the screen 8.

In this conventional image display device as described above, thehorizontal deflection electrode 6 and the vertical deflection electrode7 are both comb-shaped and spread out. Since the distance to the screen8 is longer than the distance between the horizontal and verticaldeflection electrodes, the electron beam can be irradiated ontoarbitrary positions of the screen 8 with small amounts of deflection.Therefore, with this configuration, it is possible to decrease thedistortion for both horizontal and vertical deflection.

The screen 8 is made of a glass pane, and the R,G and B primary colorphosphors which emit light due to irradiation with the electron beam areapplied in a stripe-like shape separated by black guard bands (blackmatrix) onto the rear side of this glass pane, with a metal backingarranged on top (not shown in the drawings). In FIG. 6, the broken linesdrawn on the screen 8 show the vertical sections, displayed incorrespondence to the plurality of linear cathodes 2 a to 2 s. Further,the alternate-long-and-two-short dash lines indicate the horizontalsections displayed in correspondence to the plurality of conductiveboards 15, which make up the control electrode 4.

In one section, partitioned by both (the broken lines and the alternatelong and two short dash lines), as shown enlarged in FIG. 7, two groupsof primary color phosphor stripes 20 R, 20 G and 20 B of R, G and B areapplied vertically in stripe-like shapes, separated by black guard bands22 in the horizontal direction. The horizontal lines are formed for 12lines in the vertical direction. The size of one section (1 unit) inthis conventional example is 1.0 mm horizontally, and 4.4 mm vertically,but for illustrative reasons, the lengthwise and crosswise proportionsin FIG. 7 are different from the image that appears on the actualscreen.

However, in this conventional image display device above, due to thermalexpansion of the structural elements when operating the image displaydevice, misalignments between the screen and a group of flat electrodesoccur, and due to environmental magnetic fields (for example the earth'smagnetism at that position) deviations of the beam track between thegroup of flat electrodes and the screen occur, causing misalignmentsbetween the beam spot and the phosphor stripes on the screen, resultingin a deterioration of the image quality, such as color misalignments,etc.

DISCLOSURE OF INVENTION

It is an object of this invention to solve the above-mentioned problems,and to provide an image display device, wherein misalignments of thebeam spot position with respect to the phosphor stripes on the screen,which are caused for various reasons, are eliminated, and imagedeterioration, such as color misalignments, does not occur, which isachieved by detecting the relative position of the beam spot withrespect to the phosphor stripes, and performing a correction based onthe detected value.

An image display device in accordance with the present invention thatachieves these objects includes an emission source for electron beams; adisplay screen having a phosphor layer, wherein phosphors are formed ina certain pattern and separated by a black matrix; an electron beamtrack controlling system, the system having the function of selectivelyirradiating the electron beams onto predetermined positions of thephosphor layer, and is characterized in that it includes a system foroscillating a predetermined one of the electron beams; a system fordetecting an emission amount at a predetermined position of the phosphorlayer generated by the oscillating electron beam; a system forrecognizing a misalignment of the electron beams based on the emissionamount; and a system for correcting misalignment of the electron beamsby feedback of the misalignment to the electron beam track controllingsystem.

With the image display device of this invention, these electron beammisalignments can be eliminated by making it possible to recognize theseelectron beam misalignments by oscillating one of the electron beams,which is irradiated onto the phosphor layer, and detecting an emissionamount at a predetermined position of the phosphor layer emitted by thisoscillating electron beam, and correcting the misalignments by feedingthem back into the beam track controlling system. Thus, with the imagedisplay device of the present invention, misalignments between a groupof flat electrodes and the screen, caused by thermal expansion ofstructural elements during operation, or misalignments between beam spotpositions with respect to phosphor stripes on the screen, caused bydeviations of the beam track between the group of flat electrodes andthe screen due to ambient magnetic fields (for example the earth'smagnetism at that location), which have been a problem in the prior art,can be prevented. As a result, a deterioration of the image quality,such as color misalignments caused by such misalignments, can beeliminated.

In the image display device according to the present invention, it ispreferable that the system for recognizing a misalignment of theelectron beams compares (i) an emission amount of the phosphor layer ata position that is defined by applying a certain offset to a beam track,which shifts the beam track with respect to a center of the phosphorlayer at a certain position, with (ii) an emission amount of thephosphor layer at a position that is defined by applying another offsetthat is opposite to the certain offset of the beam track with respect tothe center of the phosphor layer.

In the image display device according to the present invention, it isalso preferable that the system for recognizing a misalignment of anelectron beam compares (i) an emission amount of the phosphor layer at aposition that is defined by applying a certain offset to a beam track,which shifts the beam track with respect to a center of the phosphorlayer at a certain position, with (ii) an appropriate emission amount ofthe phosphor layer at that position.

In the image display device according to the present invention, it ispreferable that the system for detecting the emission amount of thephosphor layer uses a PIN photodiode.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of an image display device according to anembodiment of this invention.

FIG. 2 is a drawing explaining the principle of detecting the beamirradiation position (when there is no misalignment in the beamirradiation position on the phosphor stripes) in the image displaydevice according to an embodiment of this invention.

FIG. 3 is a drawing explaining the principle of detecting the beamirradiation position (when the beam irradiation position on the phosphorstripes has shifted to the left due to some reason) in an image displaydevice according to an embodiment of this invention.

FIG. 4 is a drawing explaining the principle of detecting the beamirradiation position (when the beam irradiation position on the phosphorstripes has shifted to the right due to some reason) in an image displaydevice according to an embodiment of this invention.

FIG. 5 is a exploded perspective view of an image display deviceaccording to another embodiment of this invention.

FIG. 6 is an exploded perspective view of a conventional image displaydevice.

FIG. 7 is a magnification of one section of the phosphors on the screenof the image display device shown in FIG. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is an explanation of an embodiment of this invention withreference to the accompanying drawings.

FIG. 1 shows an exploded perspective view of the general configurationof an image display device according to an embodiment of this invention,the place where a detecting portion for detecting the beam irradiationposition is installed in this image display device, and a block diagramof a feedback loop that controls the beam track according to the beamirradiation position at this installation place. Further, FIGS. 2 to 4are drawings illustrating the principle of detecting the beamirradiation position in the image display device shown in FIG. 1, inparticular showing a partial magnification of the image display area.

The image display device according to this embodiment shown in thedrawings from FIG. 1 to FIG. 4 (configuration of electrodes, screen,etc.) has basically the same configuration as a conventional imagedisplay device (see FIG. 6). However, the image display device of thisembodiment differs from a conventional image display device in that ithas a configuration that eliminates misalignments of the beam spotposition with respect to the phosphor stripes on the screen, which occurfor various reasons.

Area A in FIG. 1 indicates the detecting portion for detecting the beamirradiation position. In this embodiment, the lower left corner (area A)of the image display area of the screen 8 is the detecting portion fordetecting the beam irradiation position, and the beam that is irradiatedhere is the beam for detecting the beam irradiation position. As will beexplained below in detail, an offset, whose polarity is reversed foreach field, is applied to the beam track. This offset shifts the beamfor detecting the beam irradiation position by equal small amounts tothe left and right with respect to the center of the phosphor stripe,which is located at the previous irradiation position of the beam.

Referring to FIGS. 2 to 4, the following explains the principledetecting the relative beam irradiation position with respect to thephosphor stripes. In FIGS. 2 to 4, the configuration wherein phosphorstripes 20R, 20B, 20G of the primary colors (for phosphor cells) R, B,and G are lined up and separated by black guard bands (black matrix) 22,is the same as in the configuration of the conventional image displaydevice. Further, area B, which is shown in FIGS. 2 to 4, shows a regularimage display portion, and area A shows the detecting portion fordetecting the beam irradiation position. Area A is located in the lowerleft corner of the image display area, as explained above (see FIG. 1).La indicates the beam spot of the beam for detecting the beamirradiation position in the odd-numbered fields, with an offset to theleft side of the original track of the beam. Lb indicates the beam spotof the beam for detecting the beam irradiation position in theeven-numbered fields, with an offset to the right side of the originaltrack of the beam. Pa is the emission amount generated by theirradiation of the beam (La) for detecting the beam irradiation positionon the phosphor stripes in the odd-numbered fields, and Pb is theemission amount generated by the irradiation of the beam (Lb) fordetecting the beam irradiation position on the phosphor stripes in theeven-numbered fields.

FIG. 2 shows the state of irradiation of the beam for detecting the beamirradiation position on the phosphor stripes when there is nomisalignment in the beam irradiation position on the phosphor stripes.FIG. 3 shows the state of irradiation of the beam for detecting the beamirradiation position on the phosphor stripes when, for some reason, thebeam irradiation position on the phosphor stripes has shifted to theleft. FIG. 4 shows the state of irradiation on the phosphor stripes ofthe beam for detecting the beam irradiation position when, for somereason, the beam irradiation position on the phosphor stripes hasshifted to the right.

Here, if there is no misalignment in the beam irradiation position onthe phosphor stripes, as shown in FIG. 2, the surface area of theportion of the left side of the beam spot La hidden in the black stripeis equal to the surface area of the portion of the right side of thebeam spot Lb hidden in the black stripe. Therefore, emission amount Paand emission amount Pb become equal (Pa=Pb).

On the other hand, if, for some reason, there is a misalignment shiftingthe beam irradiation position on the phosphor stripes to the left, then,as in FIG. 3, the surface area of the portion of the left side of thebeam spot La hidden in the black stripe enlarges, and the surface areaof the portion of the right side of the beam spot Lb hidden in the blackstripe decreases. Thus, emission amount Pa becomes less than emissionamount Pb (Pa<Pb).

Conversely, if, for some reason, there is a misalignment shifting thebeam irradiation position on the phosphor stripes to the right, then, asin FIG. 4, the surface area of the portion of the left side of the beamspot La hidden in the black stripe decreases, and the surface area ofthe portion of the right side of the beam spot Lb hidden in the blackstripe enlarges. Thus, emission amount Pa becomes greater than emissionamount Pb (Pa>Pb).

In other words, the emission amounts Pa and Pb of the situations shownin FIGS. 2 to 4 are detected, and comparing the emission amounts Pa andPb, the existence and the direction of a misalignment in the beamirradiation position on the phosphor stripes can be determined. Then,with the feedback of the result of the comparison of the emissionamounts Pa and Pb to the horizontal beam track, a misalignment in thebeam irradiation position on the phosphor stripes can be corrected.During this time, the above-noted offset component (the offset componentin which the polarity reverses for each field to slightly oscillate thebeam for detecting a beam irradiation position to the right and left) ismaintained.

Further, as mentioned above, if the difference between the emissionamounts Pa and Pb is measured, it is also possible to determine theamount of misalignment in the beam irradiation position, but if thefeedback loop to the horizontal beam track, where the comparison resultof the emission amounts Pa and Pb is fed back, is a closed loop, and ifthere is a sufficiently large loop gain, it is not necessary to measurethe amount of misalignment, and if at least the direction of themisalignment can be detected, Pa=Pb can be attained, or in other words,the misalignment of the beam irradiation position can be madearbitrarily close to zero.

Returning back to FIG. 1, the following is an explanation of theconfiguration of the feedback loop that controls the beam trackcorresponding to the detected beam track irradiation position, based onthe principle of detecting the relative position of the beam irradiationwith respect to the phosphor stripes.

The feedback loop shown in FIG. 1 includes a circuit 31 for generating abeam track offset signal Sw, which reverses its polarity for each field,so that the beam for detecting the beam irradiation position is shiftedfor equal small amounts to the left and right with respect to the centerof the phosphor stripes located at the previous irradiation of the beam;an addition circuit 32 for adding this beam track offset signal Sw to ahorizontal deflection signal Sh (which is applied to the horizontaldeflection electrode, which is a system for controlling the horizontaldirection of the beam track) in accordance with the timing with whichthe beam for detecting the beam irradiation position is irradiated; aPIN photodiode 33 serving as a system for detecting the emission amountcaused by the beam for detecting the beam irradiation position; asample-and-hold circuit 34 a for sampling the emission amount Pa causedby the beam for detecting the beam irradiation position in theodd-numbered fields and holding it for the time of one field or more; asample-and-hold circuit 34 b for sampling the emission amount Pb causedby the beam for detecting the beam irradiation position in theeven-numbered fields and holding it for the time of one field or more; acomparator (differential amplification circuit with infinite gain) 35,which compares the emission amount Pa caused by the beam for detectingthe beam irradiation position in the odd-numbered fields with theemission amount Pb caused by the beam for detecting the beam irradiationposition in the even-numbered fields that are sampled and held withthese sample-and-hold circuits 34 a and 34 b and outputs a beamirradiation position misalignment signal Sd, whose polarity reverses inaccordance with the comparison result (and whose absolute value isconstant); an integrating circuit 36 for generating the beam positioncontrol signal Sc that continuously rises or falls at predeterminedspeeds, corresponding to the polarity of the output voltage of thiscomparator 35; an addition circuit 37 for adding this beam positioncontrol signal Sc to the horizontal deflection signal Sh (which isapplied to the horizontal deflection electrode, which is a system forcontrolling the horizontal direction of the beam track); a timingcircuit 38 for determining the timing for adding the beam track offsetsignal Sw to the horizontal deflection signal Sh (adjusted to the timingwith which the beam for detecting the beam irradiation position isirradiated), and the sampling timing of the sample-and-hold circuits 34a and 34 b; and a horizontal deflection electrode driving circuit 39 foramplifying to a predetermined level the horizontal deflection signal Shto which the beam track offset signal Sw and the beam position controlsignal Sc have been superimposed, and driving the horizontal deflectionelectrode 6.

The following is an explanation of the function of this feedback loop(which controls the beam track in response to the detection result ofthe eam irradiation position), with reference to FIGS. 2 to 4, inaddition to FIG. 1. In FIG. 1, by adding the beam track offset signal Swgenerated by the circuit 31 for generating a beam track offset signal tothe horizontal deflection signal Sh, the irradiation on the phosphorstripes of the beam for detecting the beam irradiation position resultsin the situation shown in FIGS. 2 to 4, but in the following, it isassumed that the beam irradiation position on the phosphor stripes forsome reason has shifted to the left, resulting in the situation shown inFIG. 3.

In this situation, the relation between the emission amount Pa caused bythe beam for detecting the beam irradiation position in the odd-numberedfields and the emission amount Pb caused by the beam for detecting thebeam irradiation position in the even-numbered fields is such that theemission amount Pa becomes smaller than the emission amount Pb (Pa<Pb).Therefore, the beam irradiation position misalignment signal Sd that isoutput by the comparator 35 has positive polarity, and the beam positioncontrol signal Sc that is output by the integrating circuit 36 starts torise.

If the structural elements for the feedback are connected in a mannerthat the beam track is shifted to the right when the polarity of thebeam irradiation position misalignment signal Sd changes to plus, thebeam irradiation position on the phosphor stripes begins to shift to theright, following the increase of the beam position control signal Sc.This shift continues to the moment when the polarity of the beamirradiation position misalignment signal Sd changes from positive tonegative, or in other words, the moment when the beam irradiationposition on the phosphor stripes changes from misalignment to the left,passing the center position of the phosphor stripes, to misalignment tothe right. Therefore, the beam irradiation position that was misalignedto the left with regard to the phosphor stripes shifts to the right, andfinally converges on the center of the phosphor stripes, as shown inFIG. 2. Further, if the beam irradiation position on the phosphorstripes is misaligned to the right (see FIG. 4), the beam irradiationposition misalignment signal Sd output by the comparator 35 becomesnegative, and since the beam position control signal Sc output by theintegrating circuit 36 starts to fall, the beam irradiation positionshifts to the left and finally converges on the center of the phosphorstripes, as shown in FIG. 2.

In the configuration of this embodiment, the error detection, that is,the comparison of the emission amounts Pa and Pb of the beams fordetecting the beam irradiation positions, is performed discretely usingthe sample-and-hold circuits 34 a and 34 b, and since there is nofunction of holding the control output, that is, the beam positioncontrol signal Sc output by the integrating circuit 36, the output ofthe integrating circuit 36 does not stop, and keeps rising or falling.Thus, even when the beam irradiation position has converged on thecenter of the phosphor stripes, strictly speaking, the beam irradiationposition still oscillates slightly to the left and right. The amplitudeof this oscillation depends on the sampling cycle with which thesample-and-hold circuits 34 a and 34 b sample the emission amount of thebeam for detecting the beam irradiation position, and the speed withwhich the beam moves over the screen, which depends, for example, on thetime constant of the integrating circuit 36, the gain of the horizontaldeflection electrode driving circuit 39, and the deflection sensitivityof the horizontal deflection electrode 6.

For example, if the field period is {fraction (1/60)} seconds, whichmeans that the comparative period of the emission amounts Pa and Pb ofthe beam for detecting the beam irradiation position is {fraction(1/30)} seconds, and if the time constant of the integrating circuit isset to a value that the beam moving speed on the screen is such that thebeam moves a distance corresponding to the width of the phosphor stripesin ten seconds, then the amplitude becomes {fraction (1/300)} of thewidth of the phosphor stripes, which is practically no problem. Further,it goes without saying that if a hold circuit is arranged between theintegrating circuit 36 and the addition circuit 37, and holds the beamposition control signal Sc for two field periods, even such smalloscillations in the beam irradiation position can be cancelledcompletely. Therefore, depending on circumstances, it is preferable thata hold circuit is arranged between the integrating circuit 36 and theaddition circuit 37, which holds the beam position control signal Sc fortwo field periods.

Thus, with the image display device according to this embodiment, thebeam irradiation position on the phosphor stripes (of a certain phosphorcell) is slightly oscillated to the left and right with respect to thecenter of the phosphor stripe by adding the beam track offset signal Sw,which is generated by the circuit 31 for generating a beam track offsetsignal, to the horizontal deflection signal Sh, thereby applying acertain offset to the beam track in the beam irradiation positiondetection portion A. Further, detecting and comparing the emissionamounts Pa and Pb generated by irradiating this beam on the phosphorstripes, it is possible to determine the existence and the direction ofa misalignment in the beam irradiation position on the phosphor stripes.Further, by sending the comparison result to the feedback loop, whichincludes the sample-and-hold circuits 34 a and 34 b, the comparator 35,the integrating circuit 36, the addition circuit 37 and the drivingcircuit 39 for the horizontal deflection electrode etc., and feedingback this result to the horizontal deflection electrode 6, which is asystem for controlling the beam track, the beam irradiation position canbe converged onto the center of the phosphor stripes.

This embodiment has been explained for the case that the beam fordetecting the beam irradiation position is arranged in the lower leftcorner of the image display area, but the present invention is notlimited to this configuration. For example, it is also possible toarrange the beam for detecting the beam irradiation position at anotherposition such as the lower right corner or the upper right corner of theimage display area.

Furthermore, this embodiment has been explained for the case that onebeam is used as the beam for detecting the beam irradiation position,but the present invention is not limited to this. For example, it isalso possible to use two or more beams for detecting the beamirradiation position. Thus, if the beams for detecting the beamirradiation position are arranged at several locations on the imagedisplay area, the average beam irradiation position on the entire imagedisplay area can be detected with more precision.

Furthermore, this embodiment has been explained for the case in whichthe phosphor pattern of the image display device is a pattern ofvertical stripes, but the present invention is not limited to thisconfiguration. Therefore, the phosphor pattern is not limited to apattern of vertical stripes, but it can also be a pattern arrangement ofphosphor cells of rectangular, circular or other shapes.

Furthermore, this embodiment has been explained for the case of amisalignment in the position of the horizontal beam irradiation, but thepresent invention is not limited to this configuration. It goes withoutsaying that it is also possible to apply the principle of this inventionto misalignments in the position of the vertical beam irradiation.

Furthermore, this embodiment has been explained for the case in whichtwo groups of R, G, and B phosphor stripes are arranged per onehorizontal section, but the present invention is not limited to thisconfiguration. For example, it is also possible to have one or three andmore groups of R, G and B phosphor stripes per one horizontal section.However, in this case, it is necessary to sequentially apply one orthree or more R, G, and B video signals to the control electrode 4, andto synchronize these signals with the horizontal deflection.

Furthermore, this embodiment has been explained for an image displaydevice, where electron beams emitted from an electron emission sourceincluding a rear electrode 1, a linear electrode group 2, a beamextractor electrode 3 and a control electrode 4 are focussed anddeflected with a focussing electrode 5, a horizontal deflectionelectrode 6, and a vertical deflection electrode 7, and irradiatesphosphors on a screen 8 to display an image (see FIG. 1). However, thepresent invention is not limited to this configuration. For example, itis also possible to apply the present invention to an image displaydevice with the configuration shown in FIG. 5. The image display deviceshown in FIG. 5 includes an electron emission source 41 that is made byarranging a plurality of electron sources 41 a in a matrix; an electrode42 (having a first comb-shaped electrode 42 a and a second comb-toothedelectrode 42 b on an insulating substrate 42 c), whose function is todeflect and focus the electron beam emitted from the electron emissionsource 41; a phosphor layer 43 that emits light when excited by theelectron beam; and a vacuum container 44 that retains the electronemission source 41, the electrode 42 and the phosphor layer 43, andwhose inside is maintained under vacuum. In this embodiment, bycontrolling the horizontal deflection electrode 6, which is a part ofthe image display device, with a feedback loop as shown in FIG. 1,misalignments of the electron beam in the horizontal direction can beeliminated, so that also in the image display device shown in FIG. 5, itis possible to eliminate the misalignment of the electron beam in eitherhorizontal or vertical direction, or both horizontal and verticaldirections, by controlling the electrode 42 with a feedback loop asshown in FIG. 1. In other words, even with the image display devicehaving a configuration as shown in FIG. 5, it is possible to apply thepresent invention, and to achieve the same results as in the embodimentexplained above.

Furthermore, this embodiment has been explained for an image displaydevice, wherein an electron beam is slightly oscillated, the emissionamount at two points in the phosphor layer irradiated by the oscillatedelectron beam is detected and compared, and based on this comparison,the misalignment of the beam is recognized and corrected. However, theresent invention is not limited to this configuration. For example, itis also possible to use a configuration for the image display devicewhere the emission amount of the phosphor layer irradiated by theoscillating beam is detected at only one location, the appropriateemission amount at this location is measured beforehand, the appropriateemission amount and the detected emission amount are compared, and basedon this comparison, the misalignment of the electron beam is recognizedand corrected.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The embodimentsdisclosed in this application are to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, all changes that come within the meaning and range ofequivalency of the claims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

The present invention prevents misalignments between a group of flatelectrodes and the screen, caused by thermal expansion of structuralelements during operation, or misalignments between beam spot positionswith respect to phosphor stripes on the screen, caused by beam trackdeviations between the group of flat electrodes and the screen due toambient magnetic fields (for example the earth's magnetism at thatlocation), which has been a problem in the prior art, by providing asystem for comparing an emission amount of a phosphor cell when acertain offset is applied to a beam track to shift the position of abeam irradiation on a certain phosphor cell (here, a phosphor stripe)with respect to the center of the phosphor cell with the emission amountof the phosphor cell when an offset is applied that is opposite to thatbeam track offset, by providing a means for feeding back the comparisonresult to an electron beam track controlling system, and by making thebeam irradiation position onto the phosphor cells of the screencontrollable by feedback. As a result, deterioration in image qualitysuch as color misalignments caused by such misalignments can beeliminated.

Therefore, according to the invention, the misalignment in the beam spotposition with respect to the phosphor stripes on the screen caused forvarious reasons can be eliminated, and it is possible to obtain an imagedisplay device in which a deterioration of the image quality such ascolor misalignments, etc. does not occur.

The image display device of this invention can be used in a broad rangeof color television receivers and terminal displays for computers, etc.

What is claimed is:
 1. An image display device comprising: an emission source for electron beams; a display screen having a phosphor layer, wherein phosphors are formed in a certain pattern and separated by a black matrix; an electron beam track controlling system, said electron beam track controlling system having the function to selectively irradiate said electron beams onto predetermined positions of said phosphor layer; a system for applying a defined offset to the electron beam track with respect to the phosphor layer at a certain position; a system for detecting an emission amount of said phosphor layer at the certain position generated by said offset electron beam; a system for recognizing a misalignment of said electron beams at an incident position, based on said emission amount; a system for correcting misalignment of said electron beams at the incident position by feedback of said misalignment at the incident position to said electron beam track controlling system.
 2. The image display device according to claim 1, wherein the system for recognizing a misalignment at an incident position of said electron beams compares (i) an emission amount of the phosphor layer at a position that is defined by applying a certain offset to an electron beam track with respect to a center of the phosphor layer at a certain position, with (ii) an emission amount of the phosphor layer at a position that is defined by applying another offset that is opposite to the certain offset of said electron beam track with respect to the center of said phosphor layer.
 3. The image display device according to claim 1, wherein the system for recognizing a misalignment at an incident position of an electron beam compares (i) an emission amount of the phosphor layer at a position that is defined by applying a certain offset to an electron beam track with respect to a center of the phosphor layer at a certain position, with (ii) an appropriate emission amount of the phosphor layer at that position.
 4. The image display device according to claim 1, wherein said system for detecting the emission amount of the phosphor layer uses a PIN photodiode.
 5. The image display device according to claim 2, wherein said system for detecting the emission amount of the phosphor layer uses a PIN photodiode.
 6. The image display device according to claim 3, wherein said system for detecting the emission amount of the phosphor layer uses a PIN photodiode. 